Electrostatic clamp, lithographic apparatus and method of manufacturing an electrostatic clamp

ABSTRACT

An electrostatic clamp for use in a lithographic apparatus includes a layer of material provided with burls, wherein an electrode surrounded by an insulator and or a dielectric material is provided in between the burls. The electrostatic clamp may be used to clamp an object to an object support in a lithographic apparatus.

FIELD

The present invention relates to an electrostatic clamp for holding anobject, a lithographic apparatus including such clamp and methods.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, e.g amask (reticle), may be used to generate a circuit pattern to be formedon an individual layer of the IC. This pattern can be transferred onto atarget portion (e.g. including part of one, or several dies) on asubstrate (e.g. a silicon wafer). Transfer of the pattern is typicallyvia imaging onto a layer of radiation-sensitive material (resist)provided on the substrate. In general, a single substrate will contain anetwork of adjacent target portions that are successively patterned.

Electrostatic clamps may be used in lithographic apparatuses operatingat certain wavelengths, e.g. EUV, since at these wavelengths, certainregions of the lithographic apparatus operates under vacuum conditions.An electrostatic clamp may be provided to electrostatically clamp anobject, such as a mask or a substrate (wafer) to an object support, suchas a mask table or a wafer table, respectively.

U.S. Pat. No. 4,502,094 (FIGS. 2 and 3) discloses a semiconductor wafer1 located on an electrostatic chuck (clamp) 2 which includes a thermallyconductive support 3, 5 made, of for example aluminum. For positioningthe wafer 1 on the chuck, locating pins 13 a, 13 b are provided so thatthe flat edge la of wafer 1 can abut pins 13 a and the rounded edge lbabuts pin 13 b so that the location of the wafer 1 is uniquely defined.The support has a peripheral portion 3 which may be 6 mm thick and athinner, perforated central portion 5 having a thickness ofapproximately 3.5 mm. The central portion has perforations or apertures6 which are circular in cross section with a diameter of 3 mm. Theelectrostatic chuck 2 also includes thermally conductive portions in theform of copper pillars 7 which are secured in the apertures 6. Thepillars 7, which are 6 mm. long and have a diameter of 3 mm, are inthermal contact with the central portion of the support and also withthe peripheral portion 3 which because of its relatively large size, canact as a heat sink.

The pillars 7 have flat end faces 8 which lie in the same fixed plane sothat the semiconductor wafer 1 can bear on them as well as on the majorsurface 9 of the peripheral portion 3 of the support. In this way, thewafer can be supported in a fixed plane relative to the electrostaticchuck 2. Moreover, because the pillars 7 are made of metal they areelectrically (as well as thermally) conductive so that the semiconductorwafer 1 is electrically contacted at its back surface (i.e. the surfacefacing the electrostatic chuck 2) by the pillars 7.

The chuck 2 also has an electrically conductive member in the form of agrid electrode 10 which may be made of, for example, aluminum.Essentially the grid 10 is circular, having a diameter of 90 mm and athickness of 1.3 mm. The meshes of the grid 10 are constituted bycircular apertures 11 which have a diameter of 5 mm. The grid 10 hasparts which extend between the pillars 7 because it is located such thatthe pillars 7 extend through the apertures 11, but the pillars 7 andgrid 10 are mutually insulated by a layer of dielectric material 12. Thelayer 12 of dielectric material which may be, for example, an epoxyresin surrounds the grid 10 so that, in addition to insulating the gridfrom the pillars 7 the grid 10 is also insulated from the centralportion 5 of the support. The separation of the grid 10 from both thepillars 7 and the central portion 5 of support 2 is, for example, 1 mm,the dielectric layer 10 filling the whole space between these variousmembers. In addition the dielectric layer is present on the uppersurface of grid 10 but this part of layer 10 has a thickness ofapproximately 200 micrometers. As explained in more detail hereinafter,the pillars 7 may protrude from the dielectric layer 12 so that thesemiconductor wafer 1 is spaced apart from layer 12 by approximately 10micrometers.

To hold the semiconductor wafer 1 against the chuck 2 a potentialdifference is applied between the wafer 1 and the grid electrode 10.Typically this potential difference is 4 kV. Electrical contact is madeto the back surface of wafer 1 via pillars 7 from the support 2 and abias potential of, for example, approximately 4 kV is applied to grid 10via an electrical connection 4 extending through the central portion 5of the support and through the dielectric layer 12. Thus anelectrostatic clamping force is established across the dielectric layer12 so that the wafer 1 is held in a fixed plane against the pillars 7 ofthe chuck 2. The magnitude of the clamping force is proportional to thesquare of the potential difference between wafer 1 and electrode 10,directly proportional to the dielectric constant of layer 12, andinversely proportional to the square of the distance between the wafer 1and the grid 10.

FIG. 3 is a plan view, taken from above, of the semiconductor wafer andthe chuck of FIG. 2 the semiconductor wafer being partially cut away.FIG. 2 shows a cross section along the line I-I′of FIG. 3. As shown inFIG. 3, the chuck 2 has a symmetrical distribution of pillars 7. Inorder to hold the wafer evenly against the chuck, it is preferable thatthe pillars 7 are relatively closely spaced to avoid localized bowing ofthe wafer. This is also consistent with the need to avoid temperaturevariations across the wafer 1. The greater the number of pillars 7 andthe closer is their spacing the more efficient can be the transfer ofheat from the wafer to the thick peripheral heat sink 3 of the support.But, as far as the number of pillars is concerned, a compromise has tobe reached because the contact pressure due to electrostatic attractionis reduced as the number of pillars 7 is increased. However, because thepillars 7 protrude from dielectric layer 12, the wafer 1 contacts thechuck 2 only at the end faces 8 of the pillars 7 and at the innerperiphery of the major surface 9. By limiting the contact area in thisway the contact pressure (i.e. force per unit area) is maximized. Thisis beneficial because the efficiency of heat transfer between the wafer1 and the pillars 7 depends on the contact pressure.

The object which is clamped on the electrostatic clamp needs topositioned with a very high accuracy on the electrostatic clamp and theposition of the object on the electrostatic clamp needs to be stableover time.

SUMMARY

It would be beneficial, for example, to provide an improvedelectrostatic clamp which gives a high accuracy and stability of theposition of the object.

According to an aspect of the invention, there is provided anelectrostatic clamp configured to, in use, hold an object in a fixedplane in a lithographic apparatus, the clamp including a supportprovided with burls whereby the top of the burls determine the plane inwhich the object is held and an electrode surrounded by an insulator isprovided in between the burls, wherein the support is made from a lowexpansion material.

According to a further aspect of the invention there is provided amethod of manufacturing an electrostatic clamp configured toelectrostatically clamp an object to an object support in a lithographicapparatus, the method including: providing a layer of material withburls; and disposing an electrode surrounded by an insulator and ordielelectric material in between the burls.

According to a further aspect of the invention there is provided alithographic apparatus including: an object support constructed tosupport an object in a beam path of a radiation beam; an electrostaticclamp configured to electrostatically clamp the object against theobject support; the clamp including a support provided with burlswhereby the top of the burls determine the plane in which the object isheld and an electrode surrounded by an insulator is provided in betweenthe burls, wherein the support is made from low expansion material.

According to an aspect of the invention, there is provided alithographic apparatus including an illumination system configured tocondition a beam of radiation; a pattern support configured to hold apatterning device, the patterning device configured to pattern the beamof radiation to form a patterned beam if radiation; a substrate supportconfigured to hold a substrate; a projection system configured toproject the patterned beam of radiation onto the substrate; and anelectrostatic clamp configured to electrostatically clamp the patterningdevice or the substrate on the respective support, the clamp including atable including a plurality of burls, the top of the burls determining asubstantially planar surface on which the patterning device or thesubstrate is held; and an electrode encapsulated by an insulator andarranged in between the burls, wherein the table is made from lowexpansion material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus in accordance with an embodimentof the invention;

FIG. 2 is a cross-sectional view, taken on the line I-I′ of FIG. 3, of asemiconductor wafer located on a conventional electrostatic chuck;

FIG. 3 is a plan view, taken from above, of the semiconductor wafer andthe chuck of FIG. 2, the semiconductor wafer being partially cut away;

FIG. 4 depicts a partial cross section of the top layer of anelectrostatic clamp according to an embodiment of the invention; and

FIG. 5 depicts a partial cross section of the top layer of anelectrostatic clamp according to a further embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus includes an illuminationsystem (illuminator) IL configured to condition a radiation beam B (e.g.UV radiation or EUV radiation); a support structure or support orpattern support (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters; a substrate table (e.g. a wafer table) WTconstructed to hold a substrate (e.g. a resist-coated wafer) W andconnected to a second positioner PW configured to accurately positionthe substrate in accordance with certain parameters; and a projectionsystem (e.g. a refractive projection lens system) PS configured toproject a pattern imparted to the radiation beam B by patterning deviceMA onto a target portion C (e.g. including one or more dies) of thesubstrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” as used herein should be broadlyinterpreted as referring to any device that can be used to impart aradiation beam with a pattern in its cross-section such as to create apattern in a target portion of the substrate. It should be noted thatthe pattern imparted to the radiation beam may not exactly correspond tothe desired pattern in the target portion of the substrate, for exampleif the pattern includes phase-shifting features or so called assistfeatures. Generally, the pattern imparted to the radiation beam willcorrespond to a particular functional layer in a device being created inthe target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” as used herein should be broadlyinterpreted as encompassing any type of projection system, includingrefractive, reflective, catadioptric, magnetic, electromagnetic andelectrostatic optical systems, or any combination thereof, asappropriate for the exposure radiation being used, or for other factorssuch as the use of an immersion liquid or the use of a vacuum. Any useof the term “projection lens” herein may be considered as synonymouswith the more general term “projection system”.

The support structure and the substrate table may also be hereinafterreferred to as an article support. An article includes but is notlimited to a patterning device, such as a reticle, and a substrate, suchas a wafer.

As here depicted, the apparatus is of a reflective type (e.g. employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g. employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines, the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery systemincluding, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL mayinclude various other components, such as an integrator and a condenser.The illuminator may be used to condition the radiation beam, to have adesired uniformity and intensity distribution in its cross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. After being reflected by thepatterning device (e.g. mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the beam onto a target portion Cof the substrate W. With the aid of the second positioner PW andposition sensor IF2 (e.g. an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theradiation beam B. Similarly, the first positioner PM and anotherposition sensor IF1 can be used to accurately position the patterningdevice (e.g. mask) MA with respect to the path of the radiation beam B,e.g. after mechanical retrieval from a mask library, or during a scan.In general, movement of the support structure (e.g. mask table) MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure (e.g. mask table) MT may beconnected to a short-stroke actuator only, or may be fixed. Patterningdevice (e.g. mask) MA and substrate W may be aligned using maskalignment marks Ml, M2 and substrate alignment marks P1, P2. Althoughthe substrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the patterning device (e.g. mask)MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the patterning device (e.g. mask table) MT and thesubstrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam is projected onto a targetportion C at one time (i.e. a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C can be exposed. In step mode, the maximum size of theexposure field limits the size of the target portion C imaged in asingle static exposure.

2. In scan mode, the support structure (e.g. mask table) MT and thesubstrate table WT are scanned synchronously while a pattern imparted tothe radiation beam is projected onto a target portion C (i.e. a singledynamic exposure). The velocity and direction of the substrate table WTrelative to the support structure (e.g. mask table) MT may be determinedby the (de-)magnification and image reversal characteristics of theprojection system PS. In scan mode, the maximum size of the exposurefield limits the width (in the non-scanning direction) of the targetportion in a single dynamic exposure, whereas the length of the scanningmotion determines the height (in the scanning direction) of the targetportion.

3. In another mode, the support structure (e.g. mask table) MT is keptessentially stationary holding a programmable patterning device, and thesubstrate table WT is moved or scanned while a pattern imparted to theradiation beam is projected onto a target portion C. In this mode,generally a pulsed radiation source is employed and the programmablepatterning device is updated as required after each movement of thesubstrate table WT or in between successive radiation pulses during ascan. This mode of operation can be readily applied to masklesslithography that utilizes programmable patterning device, such as aprogrammable mirror array of a type as referred to above.

FIG. 4 depicts a partial cross section of the electrostatic clampaccording to an embodiment of the invention. In the embodiment shown inFIG. 4, the electrostatic clamp 20 is configured to, in use, hold anobject in a substantially fixed plane 24 and includes a support or table25 provided with burls 21 whereby the top of the burls determine theplane 24 in which the object is held and an electrode 22 surrounded(e.g. encapsulated) by a dielectric 23 is provided in between the burls21. The dielectric 23 functions also as an insulator. The substantiallyfixed plane (or substantially planar surface) may correspond to a planein which the substrate is held during substrate exposure. The distancebetween the electrode 22 and the top of the burls 21 may be between 50and 1000 μm. While only two burls 21 are shown in FIG. 4 it will beappreciated that in general multiple burls may be used and that theelectrode 22 and the dielectric material 23 may be located in betweeneach of those burls 21. In an embodiment, the support 25 provided withthe burls 21 may be made form one material so that the position of theburls 21 on the support 25 is very stable and rigid which helps to keepthe object stable on its position in the plane 24. To improve thestability, the support 25 may be a factor of 10 to 200 thicker than theheight of the burls 21. For example the support may be about 40 mm thickwith a height of the burl of about 300 μm.

The top of the burls 21 determine the plane 24 (or a substantiallyplanar surface) in which the object is held. The top of the burls 21 maybe in contact with the object and this contact may require the materialof the burl 21 to be wear resistant since every time an object isclamped on the burls 21 forces are exerted on the burls 21 which maycause wear of the burls 21. Wear may make the burls 21 of the clamp 20more sensitive to sticking effects. Sticking effects are generally dueto adhesion forces between the bottom section of the object and the topsection of the supporting burls 21, as well as to electrostatic forcesgenerated by residual electrostatic charges. Adhesion forces may begenerated by material impurities, and roughness imperfectness of thecontacting surfaces. Objects may slip over the burls 21, thereby causingwear and roughness imperfection on the burls 21, which may lead toadditional sticking. Another cause of wear may be the cleaning of theburls 21 that is desirable when contaminants stick to burls 21.

The object which is clamped on the electrostatic clamp 20 needs topositioned with a very high accuracy and the position of the object onthe electrostatic clamp 20 needs to be stable over time. If copper andaluminum is used for the burls 21 and the support 25 respectively theposition cannot be guaranteed with a sufficient high accuracy becausethe thermal expansion of the metals (16.5 m/m·K×10⁻⁶ and 22.5 m/m·K×10⁻⁶respectively) is high. A high thermal expansion may give a risk tounflatness and movements in the plane 24 of the burls 21 if the clamp 20is changing in temperature. The difference in expansion coefficient ofdifferent materials used in the clamp 20 may also result in tensionsbetween the materials and in unflatness of the clamp 20. Another riskmay be that the connection between the burls 21 and the support 25 maybe too weak which makes that any tension caused by for example theelectrode 22 or the dielectric 23 may result in unflatness of the clampand/or translations of the burls 21 in the plane 24. It may therefore bebeneficial to make the support 25 and the burls 21 out of one material.The connection between the two can be made with improved rigidity if itsmade out one piece, this overcomes any tensions within the clamp 20. Thematerial of the support 25 provided with the burls 21 preferably has athermal expansion of less than about 10 m/m·K×10⁻⁶. The material may befor example SiC (Silicon Carbide as for example produced by KYOCERA™which has a thermal expansion of 4 m/m·K×10⁻⁶) SiSiC(Siliconized SiliconCarbide as produced by SAINT GOBAIN™, thermal expansion 4 m/m·K×10⁻⁶) orSi₃N₄ (Silicon Nitride, thermal expansion 3.3 m/m·K×10⁻⁶). Objects suchas substrates and reticles that may need to be clamped on theelectrostatic clamp 2 may be made of silicon and quartz respectively.Silicon has a thermal expansion of 2 to 3 m/m·K×10⁻⁶ and Quartz has athermal expansion depending on his manufacturing process of 0.05 to 9m/m·K×10⁻⁶. The thermal expansion of the clamp 20 may be chosen suchthat it is close to the thermal expansion of the objects clamped on theclamp 20 to minimize tension between the object and the electrostaticclamp 20. This results in a better flatness of the object on the clamp20 and a more stable position of the object on the clamp 2.

The materials mentioned above are also much harder than copper. The(Knoop 100 g) hardness of SiC and SiSiC is 2800 Kg/mm² corresponding toa Moh's hardness of 9-10 and Si₃N₄ has a (Knoop 100 g) hardness of 2200Kg/mm² corresponding to a Moh's hardness of 9. As described in the aboveparagraph hardness is important to avoid wear and adhesive forces of theburls 21. Copper has a Moh's hardness of about 3-5 which means it ismuch softer than the above mentioned Silicon Carbides and SiliconNitride. Substrates and patterning devices (e.g. reticles) that may needto be clamped on the electrostatic clamp 2 may be made of silicon andquartz respectively. Silicon has a Moh's hardness of between 6 and 7 andquartz has a Moh's hardness of 7 which makes that when copper is usedfor the burls 21 it is the burl that will wear. If the burls 21 wear theposition of the plane 24 may differ and the burls 21 will be sensitivefor adhesive forces.

The thermal conductivity of SiC is 120 W/m·K and of Silicon Nitride is30 W/m·K which is lower than that of cupper which is 394 W/m·K or the237 W/m·K for aluminum but in most applications this will be enough toget enough heat transport to the temperature control system. Thetemperature control system may use a water duct 27 within the support 25of the electrostatic 20 clamp to control the temperature of the clamp 2.

FIG. 5 depicts a partial cross section of the top layer of anelectrostatic clamp according to a further embodiment of the invention.In the embodiment shown in FIG. 4, the electrode 32 is surrounded by aninsulator and or a dielectric material 35, 33 and is provided in betweenthe burls 31. In the embodiment of FIG. 5 insulator material 33 isprovided underneath the electrode and the dielectric material 35 isprovided above the electrode 32. The dielectric material 35, 33 may forexample be plastics such as PARYLENE® of Para Tech Coating, Inc,KAPTON®, MYLAR® both of DU PONT™ or Liquid Crystal Polymers (LCP) whichalso work as an insulator. Quartz such as for example, SCHOTT™ sealingglass, SCHOTT™ AF37 or SCHOTT BOROFLOAT® 33 may also be used as adielectric insulator. Other materials that may be used as an insulatorand or dielectric may be Borium-nitride.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” as used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-20. (canceled)
 21. An electrostatic clamp configured to, in use, hold an object in a lithographic apparatus, the clamp comprising: a support including an upper surface and a plurality of burls extending from the upper surface, each of said plurality of burls including a top and a bottom portion, the bottom of the burls arranged on the upper surface of the support; and an electrode arranged above said upper surface and below the top portion of two burls and surrounded between said two burls by two different dielectric materials:
 22. The electrostatic clamp of claim 21, wherein the two different dielectric materials are selected from the group consisting of PARYLENE®, KAPTON®, MYLAR®, quartz, liquid crystal polymer, and borium nitride.
 23. The electrostatic clamp of claim 21, wherein the plurality of burls and the support are made of a same material.
 24. The electrostatic clamp of 23, wherein said material is a low expansion material.
 25. The electrostatic clamp of claim 24, wherein said material has an expansion coefficient of less than about 10 m/m·K×10⁻⁶.
 26. The electrostatic clamp of claim 25, wherein the expansion coefficient is less than about 4 m/m·K×10⁻⁶.
 27. The electrostatic clamp of claim 21, wherein the plurality of burls and the support are made out of one piece element.
 28. The electrostatic clamp of claim 21, wherein the electrostatic clamp includes a temperature control system.
 29. The electrostatic clamp of claim 28, wherein the temperature control system comprises a water duct.
 30. The electrostatic clamp of claim 21, wherein the support is made of a non-metal material.
 31. The electrostatic clamp of claim 21, wherein a first of the two different dielectric materials is arranged above the electrode and a second of the two different dielectric materials is arranged below the electrode and between the electrode and the upper surface.
 32. An electrostatic clamp configured to, in use, hold an object in a lithographic apparatus, the clamp comprising: a support including an upper surface and a plurality of burls extending from the upper surface, each of said plurality of burls including a top and a bottom portion, the bottom of the burls arranged on the upper surface and the top of the burls holding, in use, the object; and an electrode arranged above said upper surface and below the top portion of two burls and surrounded between said two burls by an insulator, wherein the plurality of burls and the support are made of a same low expansion material.
 33. The electrostatic clamp of claim 32, wherein said material has an expansion coefficient of less than about 10 m/m·K×10⁻⁶.
 34. The electrostatic clamp of claim 33, wherein the expansion coefficient is less than about 4 m/m·K×10⁻⁶.
 35. The electrostatic clamp of claim 32, wherein the plurality of burls and the support are made out of one piece element.
 36. The electrostatic clamp of claim 32, wherein the insulator includes two different dielectric materials selected from the group consisting of PARYLENE®, KAPTON®, MYLAR®, quartz, liquid crystal polymer, and borium nitride.
 37. A lithographic apparatus comprising: an object support constructed to support an object in a beam path of a radiation beam; an electrostatic clamp configured to electrostatically clamp the object against the object support, the clamp comprising a support including an upper surface and a plurality of burls extending from the upper surface, each of said plurality of burls including a top and a bottom portion, the bottom of the burls arranged on the upper surface of the support; and an electrode arranged above said upper surface and below the top portions of two burls and surrounded between said two burls by two different dielectric materials.
 38. The lithographic apparatus of claim 37, wherein the two different dielectric materials are selected from the group consisting of PARYLENE®, KAPTON®, MYLAR®, quartz, liquid crystal polymer, and borium nitride.
 39. The lithographic apparatus of claim 37, wherein the plurality of burls and the support are made of a same material.
 40. The lithographic apparatus of 39, wherein said material is a low expansion material. 